fixed and dynamic ip address allocation for same client

Simon Hobson dhcp1 at
Thu Feb 21 17:42:49 UTC 2008

Tarik Gasmi wrote:

>some mobile ip-devices (notebooks, pdas, mobile-ip-phones, etc.) have a
>fixed-address in one subnet, e.g. in the office, but on the other hand
>they also have to receive dynamic ip addresses from lease pools in other
>subnets, e.g. when the user is moving around on the campus to other
>when a host is configured with a fix ip-allocation
>host foo {
>   hardware ethernet <foomac>;
>   fixed-address ip-subnet1;
>it gets the ip-subnet1 when connected to subnet1. but it receives no ip
>address from a dynamic pool in subnet2 when connected to subnet2
>subnet2 <network> <netmask> {
>   ...
>   pool {
>     allow unknown-clients;
>     <some dynamic range>;
>   }

You need to reconsider your allocation rules.

"allow unknown-clients" specifically means that known clients will 
not be included, your client has a host statement, therefore it is 
known, therefore it is not eligible to receive a lease from this pool.

Is you config machine generated ? If so then it wouldn't be too hard 
to create both a host declaration (for fixed IP allocation) AND a 
subclass declaration.

        class "registeres_clients" {
          match pick-first-value (option dhcp-client-identifier, hardware);

        subclass "registered_clients" 1:aa:bb:cc:dd:ee:ff;
        subclass "registered_clients" ....

Then you can allow/deny members of "registered_clients" wherever you 
would use (un)known-clients.

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